Refrigerator system



M. E. HOUPLAIN 2,990,693

REFRIGERATOR SYSTEM July 4, 1961 2 Sheets-Sheet 1 Filed Aug. 7, 1958 M.E. HOUPLAIN REFRIGERATOR SYSTEM July 4, 1961 2 Shets-Sheet 2 Filed Aug.7, 1958 2,990,693 REFRIGERATOR SYSTEM Marcel E. 'Houplain, Paris,France, assignor of one-half to Compagnie lndustrielle des ProcedesRaoul 'Pictet,

Paris, France, a company of France 'Filed Aug. 7, 1958, Ser. No. 753,702Claims priority, application France Sept. 4, 1957 '7 Claims. (Cl.62-139) This invention relates to refrigerating systems of the typeusing an intermediate fluid ,betwen the cold source and the medium to becooled serving as 'an accumulator of the cold produced.

Refrigerating systems utilizing an intermediate fluid have already beenproposed; In one conventional system, a highly volatile intermediateliquid is used (coldgenerating or frigorigenic liquid) and the coldsource contacts the vapour phase of this iliquid while the liquid phaseis in heat-exchange relation with the medium to be cooled. Thus the heatfrom this medium vaporizes' the liquid and the resulting vapour is againcondensed by the cold source, so that negative heat units arecontinually being transferred from the cold source to the medium to becooled. However in view of the low specific heat of the intermediateliquids available, the cold build-up or accumulating capacity ofisuchsystems is extremely low.

It has been suggested, especially in connection with the rapid coolingof large amounts 'of fluid, to use a freezable liquid, such as water, asthe intermediate liquid, and immerse therein both the cold source, e.g.in the form of the evaporator coil'of a refrigerator unit, and a coolingcircuit through which the fiuid to be cooled is passed. Thus, a layer offrozen liquid forms upon the surfaces of the evaporator which provides astore of cold and is capable of melting when required, to cool the fluidto be cooled.

Systems operating on these lines have yielded poor results because heattransfer in them is essentially produced by slow convection currentswithin the non-frozen intermediate liquid, and in order to improve theheat transfer mechanical agitator means have to be provided for the bodyof liquid.

It is an object of this invention to provide an improved refrigeratingsystem of the cold-accumulating type, wherein the defects anddifliculties inherent to prior systems of this type are eliminated and,more specifically, greatly to increase the heat exchanges through aliquid medium between the cold source and the exterior medium withoutrequiring the use of external energy for agitation, such as mechanicalagitators or the like. An object is the provision of a refrigeratingsystem having a greatly increased, and controllable, accumulatingcapacity.

A system in accordanc with this invention comprises, within a sealedenclosure or tank, a solid phase, at least one liquid phase of the samesubstance asthe solid phase and at least one gaseous phase filling afree space at the top of the enclosure and comprising the vapour of atleast one liquid phase, a source of cold near the top of the enclosure,and heat exchanger means establishing a heat exchange relation betweensaid liquid phase positioned at the base of the enclosure and the mediumto be cooled, and wherein the pressure of the .free gaseousphase ispredetermined to permit the last-mentioned liquid phase to boil underthe heat imparted to it within the enclosure fromthe heat exhangermeans.

All three phases, liquid, solid and gaseous, may belong to a singlesubstance or a single mixture of substances, in which case the operatingtemperature of the system and the vapour pressure within the tank wouldsubstantially correspond to the temperature and pressure as determinedby the triple point of the substance, i.e. the point in thepressure-temperature coordinate plane at which the solid,

United States Patent time liquid and vapour phases of the substancecoexist simultaneously.

In such a case itcan be considered, disregarding temperature gradientsand variations within the system, that the cold source freezes theliquid at the temperature defined by the triple point and that theliquid, subjected only to the pressure of its own vapour, also boils atthis same temperature on receiving heat from the exchanger.

The vapour bubbles formed, which seek to reach the free upper space, arethus brought into contact with the solid phase, causing it to melt andreturn, after condensation, into the body of liquid, thereby supplyingnegative heat units to the exchanger, substantially at the temper-a tureof the triple point. I

The temperature at which boiling of the liquid sets in can, however, beincreased, i.e. the boiling retarded, by adding an inert gas into thesaid free space, so that its pressure will add to that of the vapour. Insuch case, the intense heat exchange effects occurring at the boil willfirst set in at a higher temperature level, 'in other'words the negativeheat units are yielded at a temperature higher than the freezing pointof the liquid.

The use of a single liquid in equilibrium with its solid and vapourphases may, however, pose some rather'serious difficulties in regard toregulation and control. Hence, in one desirable form of the invention,the cold accumulating function and the function of forming vapour inorder to accelerate heat exchanges, are separated from one another andtwo separate liquids are used, the one heavier and volatile, and theother lighter and readily freezable, which liquids are not miscible witheach other.

In such a case the system would comprise, in upwardly superimposedrelationship within the sealed enclosure or tank, a volatile liquid, afreezing liquid, lighter than and practically unmiscible with thevolatile liquid, and a free space at the top of the tank, with a coldsource being immersed in the freezing liquid, while the volatile liquidmay be placed in heat exchanging relation through an exchanger with themedium to be cooled.

In such a system the gaseous phase in the free space would contain atleast saturated vapour of the volatile liquid. There are two liquidphases stacked in accordance with their densities and the solid phaseconsists of the frozen part of the lighter uppermost liquid in contactwith the cold source. Just as in the case of a single liquid, reversibleheat exchange occurs between the vapour .of the volatile liquid formedon contact with the heat exchanger and seeking to reach the free space,and the saturated vapour already contained within said space, and whichon condensing will return by gravity to the bottom of the enclosurethrough the remaining freezable liquid.

These drops of condensed vapour are cooled on passing through thefreezable liquid, causing partial melting of the frozen part of saidliquid. They therefore act to cool the volatile liquid when they reachit and cause said volatile liquid to yield negative heat units throughthe exchanger to the medium to be cooled.

The tank and the heat exchanger may be so arranged relatively to eachother that the vapour of the volatile liquid formed on contact with theexchanger, is directly led to the free space at the top of the tank tocondense thereat and fall back dropwise through the freezable liquid soas to be cooled in passing through the latter. Alternatively however,the heat exchanger may be disposed within the body of volatile liquid sothat the vapour bubbles will rise directly through the freezable liquid,in which case it is possible for such bubbles to condense at leastpartly within the body of freezable liquid before they have reached thefree space. As in the first instance,

the free space may be arranged to contain only the vapour' of thevolatile liquid (as well as a small amount of the vapour of thefreezable liquid) without any added gas,

the vapour tension being at the value corresponding to the temperatureof the free upper space. This temperature is necessarily determined bythe freezing point of the freezable liquid since the free space is indirect heat exchange contact with the freezable liquid. The vapour phaseof the volatile liquid is thus in equilibrium with the liquid phasethereof, which in turn is subjected to the pressure of said vapour phaseplus the head of the freezable liquid overlying it. Now, the volatileliquid may be so selected that its vapour tension is high at thefreezing temperature of the freezable liquid, so that this additionalload or head will then be comparatively small and, on supply of heatunits from the medium to be cooled, the volatile liquid will thereforebegin to boil at a temperature only very little higher than thetemperature of its vapour phase, that is, at thetemperature of thepartially frozen freezable liquid. In such case the system will becapable of yielding cold at a temperature approximating that of thefreezable liquid.

However, just as in the case of a single liquid, the free space mayfurther contain an additional gas, and in such case the pressure towhich the volatile liquid is exposed will be increased by the pressureof this gas so that its boiling point will be correspondingly increased.In such case the transfer of cold units (negative heat units) from thevolatile liquid to the exchanger will be essentially produced throughvaporization of said liquid in contact with the exchanger, and theexchange temperature will be the temperature of the boiling point of thevolatile liquid and so may be made substantially higher, by an amount ofseveral degrees Centigrade, than what it would be in the absence ofadditional gas in the free space.

It thus is made possible to accumulate cold units at very lowtemperature and only yield them up again at a higher temperature. Thiscan be of interest for example in connection with the cooling of drinkswith water as the freezable liquid, since the optimum temperature ofcool drinks is on the order of 8 to 10 C.

In all cases therefore, regardless of whether one or two liquids areused, it is possible so to select a freezable liquid as to provide anoperating-temperature level in the system and a temperature-pressurerelationship which will determine a desired temperature level at whichthe cold units will be withdrawn from the system.

In apparatus according to the invention, the cold source may provide acontinuous cold output while the resulting cold may be withdrawnintermittently; it is only necessary that the total cold output over apredetermined period of time should equal the sum total of the amountsof cold intermittently withdrawn.

Preferably the cold production capacity of the source is selectedgreater than the average value of the intermittent amounts of coldwithdrawn and the apparatus includes means for arresting the operationof the cold source after a predetermined quantity of liquid has beenfrozen. Such means may desirably be responsive to the volume variationof the mass of freezable liquid on partial freezing, or to the resultingvariation in liquid level. Any other suitable effect may be used forcontrolling the relative quantities of the solid phase with respect tothe liquid phase in the freezable liquid.

Such control of the freezing of the freezable liquid will avoid asetting of the liquid in mass in case of an excessively prolonged periodthrough which no cold is withdrawn from the system, a condition whichotherwise would prevent normal heat exchange with the volatile liquidfrom occurring and, in case of violent vaporization of the latter, mightresult in an explosion of the apparatus.

As the freezable liquid, water may be used to advantage where thedesired temperature is in a range surrounding C., since water has a highcold accumulating capacity (80 frigories, i.e. negative calories, perkilogram ice) and moreover the substantial volume increase on freezingfacilitates regulation of the quantity of frozen liquid.

Where difierent temperature ranges are desired, other freezable liquidsmay be used, including solutions which may or may not be eutectics.

The volatile liquid used may advantageously comprise one of thechloro-fluorinated derivatives of methane or ethane commonly known inthe trade as Freons, having a high density (about 1.5) and a boilingpoint lower than normal ambient temperature. Thus Freon 114 which isdichlor-tetrafluoreth-ane has a boiling point of about 4 C. atatmospheric pressure and is practically not miscible with water, andhence is especially suitable for association with water as the freezablefluid.

The ensuing disclosure made with reference to the accompanyingdiagrammatic drawings will provide a clear understanding of theinvention but should not be construed as limiting the scope thereofotherwise than as required by the claims.

FIGS. 1 and 2 illustrate in vertical section two exemplary embodimentsof refrigerating systems according to the invention employing a singlefluid medium and suitable for use in the cooling of various fluids;

FIG. 3 is a similar view of apparatus employing two liquids; andlikewise suitable for the cooling of fluids;

FIG. 4 shows a modified construction of a two-liquid apparatus suitablefor space cooling;

FIGS. 5 and 6 illustrate two further modifications of fluid-coolingapparatus;

FIGS. 7 and 8 are temperature-pressure graphs useful in explaining theoperating principles of the apparatus described.

The apparatus shown schematically in either of FIG. 1 or 2 comprises asealed, heat-insulated tank or container 1. Near the top of the tank acold source is disposed in the form of an evaporator coil 2 of aconventional refrigerator unit not shown. Near the bottom of the tank isa heat exchanger 3 also shown as a helically coiled tube through whichthe fluid to be cooled is passed.

Now referring more particularly to FIG. 1, the tank is substantiallyfree of any gaseous contents and is substantially filled with ade-gasified aqueous liquid L contained up to a free level ZZ high enoughto submerge both the exchanger 3 and evaporator coils 2. The small freespace E above the liquid level ZZ contains essentially vapour of theliquid L. On operation of the evaporator 2, a layer of ice G forms overthe surface of the evaporator coil and the liquid L as well as thevapour in the space E is cooled to the freezing temperature of theliquid.

Thus, assuming the liquid L is pure water, a temperature-pressureequilibrium is established in the apparatus corresponding to the point Ton the temperature-pressure graph of FIG. 7. This point T is theso-called triple point at the common junction of the three curves C C Crespectively representing equilibrium between the liquid and vapourphases, the liquid and solid phases, and the solid and vapour phases. Asis well-known, the point T in the case of pure water corresponds to apressure p of 4.5 mm. Hg and a temperature t of almost exactly 0 C. Inthe temperature-pressure coordinate plane shown, the region I representsthe vapour phase, region II the liquid phase and region III the solidphase.

In such conditions, an amount of heat supplied by the exchanger willdisplace the equilibrium established at point T in the directionindicated by the arrow 1 (at constant pressure), and the water is hencecaused to boil. The vapour bubbles on entering the water cooled by theice G condense, and the condensed liquid drops back to cool the liquidcontacting the exchanger 3.

If the liquid is other than pure water, being a solution of some solublesubstance whereby the freezing point is lowered, the equilibrium curvebetween the liquid and vapour phases will not be curve C but some othercurve such as C corresponding to a lower vapour pressure, so that theequilibrium would be established with respect to the point T whichrepresents a new triple point for the set of curves .C C and .C Thesystem then operates at apressurep and .a temperature t respectivelylower than the values p andi And by suitably selecting the nature andquantity of the solid substance dissolved 'it is possible topredetermine any desired operating temperature t for the system over asubstantial range.

However, it should be noted that in an area surrounding the triple pointsuch as T or T the pressures p and p are low in'absolute value and,moreover, the curves such as C and C have a low slope, so that a verysmall quantity of gas present in the space B will be enough to altersubstantially the operating conditions of the system.

Thus, if, the pressure in said free space is p the boiling temperatureat the surface of contact with exchanger 3, which is the temperature atwhich cold is yielded up to the medium to be cooled, will equal a valuet substantially higher than the temperature t A very small amount ofinert gas added into the free space will therefore greatly .alter thetemperature at which cold units are delivered to the medium to becooled.

In the case of water and aqueous liquids which on freezing undergo aconsiderable increase in volume, on the order of the amount of iceformed at any time may be sensed by a level-sensing device responsive toimmersion into the liquid below the free surface ZZ; examples of suchdevices suitable for use therein will be described later with referenceto FIGS. 3 and 5.

The apparatus arranged as shown in FIG. 1 is suitable for use withaqueous-type liquids wherein the'volume increases on solidification.However non-aqueous type liquids may be used having different pressureand temperature coordinates of the triple point thereof, in order toachieve different operating temperatures not achievable with water andwater solutions. Such other liquids will generally show a decrease involurne on solidification, and in such cases the arrangement shown inFIG. 2 would be used wherein the evaporator 2 is positioned above thefree level ZZ of the liquid L In such an arrangement the solid will formover the surface of evaporator 2 outside thebody of liquid. Theevaporator surface may desirablybe arranged to retain the condensedliquid momentarily to promote freezing of the condensed liquid. Thesensing of the quantity of solid formed may again be effected by liquidlevel-responsive devices similar to those mentioned above but hereinresponsive to emergence of the device above the liquid level ZZ, whenthe desired amount of liquid has solidified over the surfaces ofevaporator 2.

This arrangement operates practicallyin the same way as the firstarrangement described except that :the'vapour bubbles condense-directlyupon the frozen liquid and then drop back in the form of cold drops intothe body of liquid L Again in this arrangement a small amount of inertgas insoluble in the liquid L can be used for adjusting the operatingtemperature of heatexchanger 3.

Owing to the very low vapour pressure values in the area surrounding thetriple point and the low slope of the curves such as C the vacuum intank 1 above the liquid, or the residual gas therein, has to becontrolled in a critical way. It is accordingly preferred according to afeature of the invention to use two separate liquids, the one being afreezable liquid and serving on solidification to provide the store ofcold, while the other'is a volatile liquid and hence has a high vapourpressure so that the pressure control in the system becomes much lesscritical. Thus, in FIG. 3, there is contained in the bottom of tank 1 abody of a relatively dense and volatile liquid L such asdichlor-tetra-fiuorethane (C Cl F known as Freon 114, :and the exchanger3 is immersed in it. The liquid L normally reaches up to a level XX. Thetank further contains a body of liquid L which is readily freezableandis lighter than and unmiscible with the liquid L2, so that it remainsentirely above .the level XX and reaches 6 up to a level YY such thatthe evaporator 2 is completely immersed in it. Where the liquid L isFreon 114, the liquid L may be water .or a water solution having a lowerfreezing point.

Assuming the tank was empty of air at the time the liquids L and L wereadded into it, then the free space E above the level YY is occupied bythe gaseous phase of the volatile liquid L and by a small proportion ofvapour of liquid L corresponding to the temperature of this liquid. Thepressure obtaining above the liquid L is the pressure in space E (i.e.in accordance with Daltons law the sum of the saturated vapour pressuresof both liquids L and L at the temperature under conisderation), ;plusthe weight of the liquid column of liquid L overlying the liquid L Thetank 1 is formed at its top with two sealed connections '4 and 5 throughwhich electric conductors 4a and 5a are passed, connected respectivelywith electrodes 6 and 7 positioned in the idle condition of theapparatus above the free level YY and so within the gaseous phase of thevolatile liquid L Conductors 4a and 5a are connected to terminals B andB of an alternating voltage circuit including a relay device whichnormally actuates a relay switch to closed condition in the absence ofcurrent through the circuit. Owing to the dielectric character of thevapour of liquid L particularly where this is Freon 114, no currentnormally flows through the circuit connected with terminals B and B solong as electrodes 6 and 7 are not immersed in the liquid L When voltageis applied to the cold-generating system connected with the evaporatorcoil 2, the water surrounding the coil is cooled, and begins to freezeand settle over the outer surfaces of the coil forming a solid sheath G.Owing to the increase in volume of the water on freezing the level YYgradually rises, since the level XX remains substantially unchanged.This latter statement is true, because only very low variations in thedensity of liquid L occur in the operating temperature range of theapparatus and the variations in the mass of the gaseous phase withrespect to the mass of the liquid phase are likewise very low. As therising level YY attains the electrodes 6 and 7, a circuit is establishedacross the electrodes and operates the relay to disconnect therefrigerator or cold-generating unit (not shown), from its voltagesupply. Hence, by adjusting the elevation of the electrodes 6 and 7above the free level YY in the idle condition, the amount of frozenliquid such as ice accumulated on the evaporator 2 can be controlledwith considerable accuracy. A small amount of alkaline salts or othersuitable substance may be added into the water to increase itsconductivity if required.

When a desired amount of ice has thus been built up on the evaporator,and a liquid to be cooled is flowing through the exchanger 3, heat istransferred from this liquid through the walls of the exchanger coiltube to the liquid L thereby bringing this liquid to the boil, providedthe temperature of the liquid to be cooled is higher than the boilingpoint of the liquid L as determined by the pressure in the space E andthe pressure head provided by the depth of liquid L used.

Vapour bubbles are thus created in the liquid L and rise up through theliquid L as shown at b in FIG. 3

in the portions of said liquid that are not frozen. These bubbles seekto rise through the cooler portions of liquid L adjacent to theevaporator coil 2 and through the frozen solid adhering to the coil, andin so doing the bubbles are substantially cooled and condense back toliquid form; such condensation occurring in part during upward travel ofthe bubbles through the body of water or liquid L and in part after thebubbles have reached the surface YY. 'I he vapour of the liquid L thusconverted back to a strongly cooled liquid falls back in the form ofdrops through the body of lighter liquid L owing to the substantialdifference in specific gravity between the two liquids. Such returningdrops of liquid 7 L serve to transfer cold units to the body of liquid Land thence to the heat exchanger 3. Simultaneously, the ice melts andthe level YY gradually drops again.-

After an amount of the solidified liquid L or ice has melted, the levelYY drops sufficiently to uncover the electrodes 6 and 7 and thusactuates the relay switch to place back the cold-generating unit intooperation. The instantaneous power output available from the compressoris thus added to the cold units released on fusion of the frozen liquid.The graph of FIG. 8 illustrates a typical operating cycle for such asystem.

In FIG. 8 the curves C C and C are the equilibrium curves for the liquidL having the same significance as the correspondingly referenced curvesin FIG. 7. Curve C is the liquid-vapour equilibrium curve for the liquidL As the temperature of solidification of the liquid L which, in thepressure ranges used, is very close to the temperature of triple pointT, the vapour pressure of the volatile liquid L is 2 This pressure canbe quite high, say equal to or higher than normal atmospheric pressure.Owing to the vapour pressure of the freezable liquid L and the pressurehead of this liquid itself, the pressure in space E is 2 correspondingto a boiling temperature L; in the volatile liquid. Temperature i isquite close to the temperature t owing to the relatively high slope ofcurve C, which increases as the liquid L approaches its critical point.The relatively high value of the slope of curve C, makes itsubstantially easier to add a gas into the space E than would be thecase if a single liquid were used, in order to exercise accurate controlover the operating temperature 2 of the exchanger through adjustment ofthe pressure p obtaining in the space E. Where the space E thus containsa neutral gas under pressure, such space should be made large enough sothat variations in the level YY will not substantially modify thepressure of said gas. Thus, assuming the freezable liquid is water,compression of the gas in space E on formation of ice would tend toincrease the boiling point of the volatile liquid so that the value ofthe cold temperature supplied by the system would then increase as theamount of ice contained in the system increased.

In the embodiment shown in FIG. 4 the exchanger coil 3 is omitted and anexchanger is provided outside the tank, and the entire system is adaptedto be received within a heat-isolated enclosure as indicated by thechain lines 14. The system in this embodiment is used for cooling suchan enclosure. This enclosure may, for example, constitute a cold storagechamber into which comparatively large and heavy articles areperiodically introduced and have to be rapidly cooled. It will beunderstood that in such an arrangement where the entire system isreceived within the enclosure to be cooled the walls of tank 1 need notbe heat isolated.

The exchanger 13 in this embodiment comprises a conduit connected withthe bottom of tank 1, and leading to a circuitous coil section providedwith radiating fins having its other end connected with the top of thetank in the free space E thereof. Liquid evaporated in the exchanger 13is thus directly delivered in vapour form to the free space E where itcondenses and falls back in liquid drops to the bottom of the tank 1. Toavoid entrainment of the liquid with the vapour bubbles, an expansionchamber 13a may be interposed in the circuit 13 at an elevationcorresponding to the particular level to which the liquid L rises in theidle condition of the system to balance the pressure head of the liquidL In the embodiment shown in FIG. 5 means are provided for guiding theconvection currents including both the upward flow of the vapour bubblesand the downward flow of the condensed drops of liquid L such guidemeans being in the form of a vertical cylindrical sleeve 8 extendingcoaxially in the tank and including an upper section surrounded by theevaporator coil 2 and an enlarged bottom section surrounding theexchanger coil 3.

Further, in this embodiment, a different arrangement is used from thatheretofore described and shown in FIGS. 3 and 4 for controlling theamount of frozen liquid allowed to form. The ice build-up control meansnow about to be described have the advantage of averting theintroduction of gas into the free space at the top of the tank.

The ice build-up control means here used comprise a resistance Rimmersed in the freezable liquid, while a resistance R having a hightemperature coefiicient of resistance, such as a thermistor, is arrangedsomewhat above the level YY. Both resistances have one end connected toan outer terminal B connected with the refrigerator unit controlcircuit, while the other ends of the resistances are connected to therespective outer terminals B and B These terminals are respectivelyconnected to the one ends of resistances R and R connected to the othercontrol circuit terminal B Thus the four resistances form a Wheatstonebridge which is arranged to be normally balanced and which will becomeunbalanced in one or the other sense as the temperature responsiveresistance R becomes immersed in or emerges out of the liquid. Ifsuitable relay means are connected across terminals B and B it will thusbe possible to arrest the operation of the cold-generating apparatus ona change in temperature of the resistance R due to a variation in thelevel of the plane YY. It should be noted that the level sensing devicejust described, which has the advantage of utilizing only the differencein specific heat and heat conductivity coefficients of a liquid and agas, may if desired be used as the level-responsive means in otherembodiments of the invention, e.g. in FIGS. 1 and 2.

Yet other equivalent liquid-level-responsive electric circuit controldevices such as, for example, well known float switches, may of coursebe used than those described.

In the modified construction shown in FIG. 6, the evaporator 2 andexchanger 3 are positioned in two separate tanks 9 and 10, e.g. of thehorizontal cylindrical form shown in superimposed relationship to eachother, and connected by vertical tubes 11 and 12 at their ends. Thetubes respectively serve to convey the rising vapours from the liquid Land for the downflow of the condensed liquid L as indicated by arrows.Tube 11 rises up to a point near the top of tank 9 and tube 12 extendsdown to a point near the base of tank 10.

It will be apparent that many further variations and modifications maybe conceived by those familiar with the art without exceeding the scopeof the ensuing claims.

What I claim is:

l. A refrigerating system comprising sealed container means; a firstbody of a relatively heavy volatile liquid filling the lower part ofsaid container means; a second body of freezable, lighter liquidoverlying said first body in said container means, a substantialliquid-free space remaining in said container means above the liquidlevel of said second body; cooling means immersed in said second bodyand capable of freezing the liquid of said second body; heat exchangemeans associated with a medium to be cooled and in heat exchangerelation to said first body of liquid; and means responsive to variationof said liquid level for controlling operation of said cooling means.

2. A refrigerating system comprising a cooling plant having anevaporator; sealed container means; a first body of a relatively heavyvolatile liquid filling the lower part of said container means; a secondbody of tfreezable, lighter liquid overlying said first body in saidcontainer means and enclosing said evaporator, a substantial liquidfreespace remaining in said container means above the liquid level of saidsecond body; heat exchange means associated with a medium to be cooledand in heat exchange relation to said first body of liquid; and meansresponsive to variation of said liquid level for controlling operationof said cooling plant.

3. A refrigerating system according to claim 1 wherein said second bodyof liquid is an aqueous liquid.

4. A refrigerating system according to claim 1 wherein said second bodyof liquid is an aqueous liquid, and said first body of liquid is aFreon.

5. A refrigerating system according to claim 1, wherein said heatexchange means comprises a cooling coil fully immersed in said firstbody of liquid and having said medium to be cooled flowing through saidcoil.

6. A refrigerating system according to claim 1 wherein said heatexchange means comprises a duct extension of said container means, thelower part of which duct extension partly contains said first liquidbody and the upper part of which is in communication with saidliquidfree space.

7. A refrigerating system according to claim 1, wherein said containermeans comprise two superimposed communicating containers respectivelycontaining said liquid bodies, the communication comprising an upwardlydirected duct starting from an upper part of the lower one of saidcontainers and directed toward an upper 10 inner part of the upper oneof said containers and a downwardly directed duct starting from a lowerpart of the upper one of said containers and directed toward a lowerinner part of the lower one of said containers.

References Cited in the file of this patent UNITED STATES PATENTS1,700,429 Bright Jan. 29, 1929 1,744,968 Keith Jan. 28, 1930 2,022,764Gibson Dec. 3, 1935 2,083,396 Philipp June 8, 1937 2,095,008 PhilippOct. 5, 1937 2,142,828 Smith Jan. 3, 1939 2,142,856 Lieb Jan. 3, 19392,146,058 Doyle Feb. 7, 1939 2,219,789 Potter Oct. 29', 1940 2,674,101Calling Apr. 6, 1954 FOREIGN PATENTS 651,939 Germany Oct. 22, 1937

